Multiple lumen catheters are in clinical use as blood access devices for easy and safe connection to hemodialyzers, or other blood treatment devices. Their use is desirable for chronic medical conditions, where frequent treatment of the blood of a patient is required, requiring frequent access to the vascular system.
Such catheters have a distal end which is implanted typically in a vein of the patient, while the proximal end of the catheter, when in use, communicates with a tubular set or the like which permits the circulation of blood from the vein, through the catheter, and through the set to a blood processing device such as a hemodialyzer. Then, the blood moves through typically another tubular set back to another lumen of the catheter, and then back to the vein of the patient.
Jugular and subclavian multiple lumen catheters are typically intended as permanent blood access devices. Femoral catheters are typically used as an intermediate-term blood access devices, which are expected to be removed after a period of time.
In the clinically used double lumen catheters for hemodialysis, the lumen for outflow of blood back into the vein terminates approximately 20-30 mm. beyond the lumen for inflow, which draws in blood. The purpose of this is to prevent direct recirculation of blood, which is when blood returned by one catheter lumen flows directly into the other catheter lumen again. This, of course, reduces the efficiency of the blood treatment process. This is the case for the catheters which are clinically used, and also are illustrated in Mahurkar U.S. Pat. No. 4,895,561; Martin U.S. Pat. No. 5,156,592; and Twardowski et al. U.S. Pat. No. 5,209,723.
Other multiple lumen catheters have flush ends in which the distal ends of the lumens terminate at the same longitudinal position along the catheter, such as in Sisley et al. U.S. Pat. No. 4,405,313. However, these catheters are not used for the withdrawing and reintroducing of large amounts of blood of a patient as is done in hemodialysis. Rather, such catheters are for the infusion of medications and/or parenteral nutrition, with only the occasional withdrawal of a sample of blood. Thus, the issue of direct blood recirculation is not a problem, and there distal end thus is designed without regard to solution of the blood recirculation problem.
The catheters for hemodialysis require high blood flows of typically 200 ml per/min or more for efficient dialysis. The direct recirculation of blood as defined above causes a reduction in the effective blood flow and thus decreases the efficiency of dialysis. Essentially, each percent of blood recirculation that is present in a catheter decreases the effective blood flow by the same one percent, which, of course, reduces the efficiency of dialysis.
In multiple lumen catheters, direct blood recirculation values of less than 15 percent are generally deemed acceptable. To achieve this, in the prior art it was believed to be mandatory to longitudinally space the distal ends of the inlet catheter lumen and the outlet catheter lumen by about 20-30 millimeters in order to avoid unduly high direct recirculation. However, several disadvantages have been noted by such large longitudinal spacings between the distal ends of the respective lumens. For example, it may be desired to reverse the blood flow through the lumens because the usual inflow lumen is not delivering sufficient blood flow due to clotting. The only other alternative is to remove the catheter. In this circumstance, the widely spaced lumen ends do not work well in that and recirculation values rise to undesirable levels. Also, it has been found that blood clots can and do attach immediately distal to the inflow lumen when there is a wide longitudinal spacing between the two distal ends of the catheter lumens.